1. Field of the Invention
The present invention relates to opaque and pearlescent, laminated and stretched products composed chiefly of a polypropylene. The present invention is concerned more specifically with opaque and pearlescent, laminated and stretched products obtained by laminating together a first layer opacified by adding a specific petroleum resin having a high softening point to a crystalline polypropylene and a second lustrous layer comprising a crystalline polypropylene, and a method for making them. In the present disclosure, the term "products" means sheet, film, yarn or filaments obtained by slitting such film as above, and molded products of sheet, film, etc.
2. Statement of the Prior Art
In general, pearlescent or opaque products having the form of uniaxially or biaxially stretched films are widely used as general-purpose packaging material, ornamental material, synthetic paper or transcription printing paper etc. or as packing material, weaving yarns, etc. in the form of tapes, ribbons or filaments, or even as hollow containers for various articles.
As heretofore known in the art, imparting pearlescence or opaqueness to products has generally been achieved by:
(1) adding to polypropylene lustering materials such as white pigments, extender pigments or pearl essence etc.,
(2) providing a large number of foams in products by adding foaming agents to polypropylene during molding,
(3) adding inorganic fillers in a large amount to polypropylene and, then, stretching them to provide voids in them-see Japanese Patent Publication No. 63(1988)-24532 and Japanese Patent Laid-Open No. 63(1988)-117043-and
(4) treating molded products with solvents or chemicals etc. to make them dull.
These techniques, however, have the following drawbacks. That is, problems with the first technique are that it is difficult to obtain pearlescence with white pigments and extender pigments, and pearl essence is very costly and moreover has to be added to polypropylene in a large quantity. With the second technique, it is difficult to provide uniform and fine foams in thin products such as films, because the foams have a tend to become large in size. A problem with the third technique is that, since the inorganic fillers are added to polypropylene in large quantities, there is a great deal of drop of fluidity during extrusion or occurence of clogging of a screen pack. Another problem is that the inorganic fillers tend to absorb moisture, causing poor dispersion of the inorganic filler and generation of foams in the products, and the replacement of resins in the molding-machine takes much time. Yet another problem is that the product becomes ill-lustered and roughened on its surface. A problem with the fourth technique is that a treating step needs to be provided separately after a forming step and further needed are a step of removing the solvents and chemicals, suffering from a disadvantage in terms of the equipment and expense. Another problem is that the product thus produced has a dull touch and is ill-lustered.
An object of the present invention is to provide opaque and pearlescent, laminated and stretched products which are free from the above-mentioned defects of the prior art.
As a result of an extensive investigation, the inventors have already found that stretching under specific conditions of polypropylene to which a specific amount of a petroleum resin having a specific high-softening point is added can give light-weight stretched products of opaqueness and pearlescence, which are better in formability than conventional ones, and filed a patent application for them (Japanese Patent Application No. 1(1989)-74919). The products thus obtained by this method are better than conventional ones. However, their surface luster or pearlescence was still less than satisfactory for ornamental purposes. Further studies have now revealed that the above-mentioned object is achieved by the provision of products in which a layer of surface gloss, comprising a specific crystalline polypropylene, is laminated on an opaque layer comprising a crystalline polypropylene and a specific petroleum resin with a high softening point, thereby improving its surface gloss considerably.